This week on "Our World" ... How forests influence Earth's climate ... A novel way to help purify drinking water ... and some facts about glaucoma, the "sneak thief of sight" ...

FRIEDMAN: "It's a challenge making the decision on whether to operate or treat with medicines and lasers, and it's a big challenge in developing countries, where there may not be as easy access to either."

The respected journal Science devotes a good chunk of this week's issue to a special section called "Forests in Flux."

Forests cover about 30 percent of the Earth's land area, and they play a major role in the planet's climate.

The seven articles look at the forests of the past, managing forests to reduce the impact of climate change, and other topics. We spoke with authors of two of the papers.

We'll hear from Robin Chazdon, who wrote about forest restoration, in a moment.

But first, there's the question of how forests affect climate. The answer is, in a number of ways. And different kinds of forests affect climate differently.

Gordon Bonan of the National Center for Atmospheric Research in Colorado says there is a scientific consensus that human activity is contributing to global warming.

BONAN: "But what we don't know yet is how forests, and changes in forests as climate changes, will feed back to affect climate. In some cases that can be a benefit to us and mitigate climate change. In other cases it could be to the detriment and actually accentuate the climate change."

For one, forests serve as reservoirs of carbon. Growing plants take in carbon dioxide, which is a greenhouse gas. When they die, they release the carbon — slowly as they rot, or quickly if they're burned.

Another way forests affect climate is through evaporation, which can have a cooling effect.

A third process has to do with albedo — how reflective the land is. Forest-covered land is generally darker than barren land, so it absorbs solar radiation.

It gets more complicated, still. A tropical forest is different from a temperate forest, and boreal forests, found at higher latitudes, are different still. Each influences climate in different ways. The biggest impact, Bonan says, comes from the tropical and boreal forests.

BONAN: "The boreal forest has a large impact on climate because of its low surface albedo. And this keeps the climate warmer than if the trees weren't present. In the tropics, we know that the tropical forests are absorbing carbon from the atmosphere, and that deforestation of tropical forests releases that carbon to the atmosphere. These two forests are actually very important to the climate, but for different reasons."

Forests have traditionally been valued for their biodiversity, as a source of wood products, in helping maintain water quality, for their recreational and even their spiritual value. But Gordon Bonan of the National Center for Atmospheric Research says their role in managing climate has not been appreciated, especially by non-specialists.

BONAN: "And so as we begin to think about crafting policies to mitigate climate change, we need to better understand what forests do to the climate and how to manage them."

One part of forest management involves restoration after they've been damaged or destroyed, whether by nature or by people. Robin Chazdon of the University of Connecticut writes about that in her paper in Science.

CHAZDON: "We have depleted long-term sources of carbon. We need to really put them back. And the only way to do that is to allow slow-growing trees to accumulate carbon over time in their tissues and to keep that stored in their tissues. Those trees are also putting a lot of carbon back into the soil, and soil is a huge reservoir of carbon. And we need to really think long-term about this in terms of trying to counter carbon losses in the planet."

But she cautions that not all forests are the same. Single-crop plantations are no substitute for diverse natural forests. And Chazdon says even thoughtful and well-intentioned reforestation programs can come up short.

CHAZDON: "I think that there's a lot of promise in restoring forests, but I would caution that we can not really bring back the original forests. The types of forests that are being destroyed have developed over hundreds or thousands of years in some cases. And we can't, in the blink of an eye recreate that kind of diversity and stature."

Robin Chazdon of the University of Connecticut. As the editors of Science put it, these authors and the others writing about forests this week "make clear why we must better understand and maintain these complicated but vital forest systems."

Scientists are reporting in this week's New England Journal of Medicine that they have made an experimental vaccine against a dangerous strain of avian influenza that is not only potent but can be stockpiled quickly. The drug is made using the cells from monkeys instead of chicken eggs. VOA's Jessica Berman explains.

BERMAN: Millions of doses of stockpiled vaccine to protect people around the globe against a highly virulent H5N1 bird flu pandemic, if and when one should occur, are made using the embryos of hens' eggs.

Peter Wright is a professor of pediatrics at Dartmouth College in Hanover, New Hampshire.

WRIGHT: "Although it is the best we have, it's probably not, in my opinion — and this is very much a perspective that reflects my opinion — is not yet where we want to be in terms of having a vaccine that we can roll out in the next several months to a year if we had to."

BERMAN: Wright says because chickens lay most of the eggs in the spring, the vaccine production method, which was developed a half century ago, limits how many doses can be produced.

Wright says an experimental vaccine that's produced using monkey cells begins to address some of the problems with the current stockpiles of avian flu vaccine.

Hartmut Ehrlich is with Baxter Bioscience in Vienna, Austria, and is the study's lead author.

Ehrlich says using primate cells to make the vaccine could significantly reduce the amount of time it takes to manufacture the vaccine.

EHRLICH: "That means from the time we and other manufacturers are getting the pandemic strain for producing the vaccine, it will take us about twelve weeks less. So that translates into three months to have vaccine ready to be shipped out."

Meanwhile, global health officials remain concerned that millions of doses of avian flu vaccine that have been stockpiled for years in anticipation of a bird flu pandemic are beginning to lose their potency.

Officials are calling for adjuvants, or additives, to be set aside to strengthen the vaccines. Jessica Berman, VOA News, Washington.

One of the most pressing global problems is ensuring an adequate supply of safe, clean drinking water. In many places, drinking water is contaminated by bacteria, fungi and viruses, rendering it unsafe for consumption. Water treatment technologies exist, but many are expensive or they're too slow to supply enough water to the many people who need it. Rose Hoban reports on a novel approach to addressing the problem.

HOBAN: Environmental engineering professor Claudia Gunsch from Duke University in North Carolina has been trying a new approach to the problem of water purification. She's working with something called RNAi — that stands for RNA interference. It's a genetic technology already in use to treat cancer.

GUNSCH: "The RNAi is a single-stranded piece of RNA, and it binds to another single-stranded molecule of RNA in the cell. And when it binds, it inactivates it and gets chopped up into smaller pieces, rendering it inactive. And so, if you can target a gene that is essential for the cell to function, then you're essentially disabling that microorganism."

HOBAN: Gunsch targeted genes present in the kinds of harmful bacteria commonly found in water. She's one of the first people to use RNAi in this way.

GUNSCH: "We have taken cells and mixed some of this RNAi in a single container and then we've monitored for the activity of specific genes. And so we have a nice reporting system, which is based on color, and so it makes it very easy to determine what the activity of that gene is. So it goes from yellow to clearer, for instance. So it makes it really easy for us to see if it's working."

HOBAN: Gunsch says so far, she's only treated small quantities of water at a time. For large-scale operations, she says it might be possible to integrate the RNAi into a filter. For example, it could be part of a carbon filter that would de-activate chemical toxins as the RNAi killed microorganisms.

GUNSCH: "Currently in many developing nations, they're using just sunlight to inactivate pathogens, so they put water in glass bottles and they put them on their roofs of their house and leave them out there for, you know, several hours and then rotate them every so frequently and the sunlight kills the pathogens. And, so that works fairly well, but you would be able to integrate this hopefully with these filters and get a much higher removal efficiency for them."

HOBAN: Gunsch says she's several years away from something that could be used on a larger scale, but she believes this new technology holds promise.

Gunsch's co-author, Sara Morey, presented their research in Boston recently, at the annual meeting of the American Society of Microbiology. I'm Rose Hoban.

Time again for our Website of the Week, when we showcase interesting and innovative online destinations.

This week, it's the website of an organization whose studies and public opinion surveys paint a vivid portrait of Americans and what they think — the Pew Research Center.

ALLEN: "You won't find many opinions here. You'll find a lot of facts, though. And I think facts are interesting."

Jodie Allen is an editor at PewResearch.org, which charts trends in demographics, journalism, economics, the environment, and many other fields.

ALLEN: "Religion is always a big draw. The Internet things are always of interest. And of course our political polls are, too. I don't want to downplay that. But the social and demographic trends, like we just put out a survey on how the middle class is doing and where the stresses and strains are coming from — that was a big draw."

Browsing Pew's surveys and analyses can give you a good start toward understanding what's going on in the United States.

In recent weeks, PewResearch.org has posted reports on religious belief and the brain, how the economy has displaced Iraq as a political issue, and the Internet's role in consumer decision-making.

Pew also does surveys around the world, and at PewResearch.org you can see the latest assessment of global opinions.

ALLEN: "This past week we just put out the first report from our most recent global attitudes survey on two things, primarily: attitudes toward America and Americans, and secondly, attitudes toward China."

Pew editor Jodie Allen also highlights the site's Daily Number. Here's one from this past week: 20 percent. That's the percent of adults under age 30 who say being wealthy is a top priority for them. The percent declines among older Americans, but non-whites and immigrants think it's more important to be rich.

Get more facts in a fascinating look at issues and trends in American life and world opinion at PewResearch.org, or get the link to this and more than 200 other Websites of the Week from our site, voanews.com/ourworld.

We haven't had time recently to dip into the Our World mailbag to answer one of the many science questions we get.

So let's remedy that right now with an email from Nze Abbott Agunwah, who writes from somewhere out in cyberspace. He wants to know about a disease that can cause blindness if it's not treated — glaucoma.

For some answers we checked in with Dr. David Friedman, associate professor of ophthalmology at Johns Hopkins University in Baltimore. He's also worked in developing countries with humanitarian NGOs devoted to eye health, including Orbis International and Helen Keller International.

FRIEDMAN: "Glaucoma is a disease that affects the nerve in the back of the eye. That nerve is the part of the eye that connects the eye to the brain."

Q: What causes the disease?

FRIEDMAN: "Glaucoma most commonly is caused by damage to the cells in the back of the eye that occurs when the pressure in the eye is too high. So just like a balloon can be inflated too hard, the eye in a sense can be too hard for the optic nerve."

Q: So, how is it diagnosed typically?

FRIEDMAN: "In developed countries, one way that people screen is through eye pressure. Unfortunately, even though high eye pressure is associated with a much higher rate of disease, about half of those people who have glaucoma have pressures that are in the normal range. The best way to diagnose glaucoma is to have a thorough eye exam, where a qualified observer looks at the optic never and can tell that it's been damaged in a characteristic way."

Q: Looked at it visually?

FRIEDMAN: "Yeah, you have to look at it. Unfortunately, glaucoma is often completely without symptoms. So the patient walks around fine until it's fairly advanced. Glaucoma's known as the sneak thief of sight."

Q: "Sneak thief of sight." Well, I guess that gets to the question of treatments. What treatments are available?

FRIEDMAN: "Glaucoma is, as of today, treated completely by treating the eye pressure. We know that eye pressure causes glaucoma, even in patients with lower pressure. And the main ways that we treat pressure are with eye drops; there are lasers, and there are surgeries where we actually have to cut on the eye, to let fluid out of the eye."

Q: Once the nerve is damaged, though, is it reversible?

FRIEDMAN: "The damage to the nerve is permanent and does not reverse, but the worsening of the disease can usually be stopped."

Q: Surgery is obviously more expensive than drops, but are we talking about very sophisticated and expensive procedures and medicines?

FRIEDMAN: "The big issue in developing countries is the affordability of medicines. Surgery can lower [eye] pressure and it's a one-time event, but it has more risk. You can lose vision from surgery. It's a challenge making the decision on whether to operate or treat with medicines and lasers, and it's a big challenge in developing countries, where there may not be as easy access to either."

Q: Well, having worked with Orbis and Helen Keller and other NGOs, what sort of programs exist to bring this higher level of care to patients in developing countries?

FRIEDMAN: "I think the main focus right now in developing countries is on making sure that we're not missing the people that are coming through that already are getting an eye exam and trying to guarantee that if they have glaucoma, they're identified. And so what we're really focusing on right now is training, making sure there are doctors that have the skills and ability to recognize the disease, and to treat the disease, to have the surgical skills as well."

Dr. David Friedman of Johns Hopkins University says that not everyone is at equal risk for glaucoma. Older people are at higher risk, as are certain racial groups, particularly people of African descent.

If you have a science question we can answer, please send it in. We can't answer them all, but we do try to present some of the most interesting ones we get. You can email your question to ourworld@voanews.com, or listen for our postal address at the end of the show.

And finally today, many fruit, nut and berry crops depend on honey bees for pollination, but more and more bee hives are dying each year. Parasites, viruses, and pesticides may all play a role, but as Véronique LaCapra reports, researchers are still baffled by what they call colony collapse disorder.

LaCAPRA: Honey bees are the most valuable pollinators of agricultural crops worldwide. In the United States, approximately 130 crops depend on honey bees for pollination. Their work is worth about $15 billion a year.

VANENGLESDORP: "We estimate that one in every three bites of food we eat are directly or indirectly pollinated by honeybees."

VANENGLESDORP: "Honeybees are the movable pollination force in modern agriculture."

LaCAPRA: Almonds, blueberries, and apples; carrots, onions, and squash - all of these fruits and vegetables grow in different parts of the country and bloom at different times of the year. So, to meet the pollination demand, commercial beekeepers truck their hives around the country. A single beekeeper may move tens of millions of bees, covering thousands of kilometers in a single trip.

VANENGLESDORP: "So all your fruits and vegetables, all your flowering plants require insect pollination, and honey bees do a majority of that pollination."

LaCAPRA: In the 1940s and '50s, there were approximately five million managed bee colonies in the United States. Today, that number has dropped to less than half that. Severe declines began in the 1980s, with the accidental introduction of a new parasite called the varroa mite.

VANENGLESDORP: "It's actually an amazingly large parasite. If we were a bee, it would be like a dinner plate feeding on us. It has these very sharp mouthparts that pierce the skin or exoskeleton of the bee. And actually it spits inside the bee, and in that spit we believe that there's a protein which acts a lot like AIDS virus does in the fact that it breaks down the insect's immune system."

LaCAPRA: The mite can also transmit viruses and other pathogens from bee to bee, and wipe out entire colonies.

VANENGLESDORP: "This is our biggest challenge, and it still kills most of the colonies in the country."

PETTIS: "And what you want to do, the way you're going to get stung — no, I'm just going to tell you so that you'll — no, no, I'm just saying, the way you would get stung, is as you grab this frame?"

LaCAPRA: Jeff Pettis is the lead scientist at the U.S. Department of Agriculture's Bee Research Lab, just outside of Washington, D.C.

PETTIS: "So, just pick it up ... and you're a beekeeper."

LaCAPRA: Pettis and his team have been studying a more recent and mysterious threat to honey bee colonies.

PETTIS: "We're suffering probably 15-20 percent losses normally throughout the year of honeybee colonies. Our last two years we've been over 30 percent losses, and so this is what we're calling this phenomenon of CCD, colony collapse disorder."

LaCAPRA: CCD looks very different from other causes of bee death, and it happens much more quickly: within just a few weeks, most of the adult worker bees disappear from the hive, leaving the queen and all the young bees behind.

Since CCD was first reported, researchers have been scrambling to find a cause.

PETTIS: "We've done enough looking and testing and sampling of the bees that are there, that if we had one single novel pathogen or problem, that we would already have identified it. We think it's a complex, maybe even a syndrome - things that are coming together to cause the losses of bees."

VANENGLESDORP: "What's really frightening about this new condition is we don't know what causes it, so we don't know how to stop it."

LaCAPRA: The lack of clear answers worries Dennis VanEnglesdorp.

VANENGLESDORP: "These large migratory [bee keeping] operations, which we rely on to move across the country in order to pollinate these different crops, are in real danger, because they can lose 30, 50, sometimes 80 percent of their colonies. They can absorb a loss like that one year in a row, maybe two years in a row, but they can't do it three years in a row and stay in business."

LaCAPRA: And bee declines are not limited to the United States.

VANENGLESDORP: "We are hearing reports from Europe, from Canada, and from South America, even some from Asia, where honeybee populations are collapsing and decreasing."

LaCAPRA: There are still enough bees in the U.S. to meet demand. But VanEnglesdorp warns that continued colony losses could threaten the production of some crops, and drive more and more beekeepers out of business. For Our World, I'm Véronique LaCapra.

MUSIC: "Our World" theme

That's our show for this week. If you'd like to get in touch — maybe you have a science question for us — email us at ourworld@voanews.com. Or use the postal address —

Our WorldVoice of AmericaWashington, DC 20237 USA.

Faith Lapidus edited the show. Eva Nenicka is the technical director. And this is Art Chimes, inviting you to join us online at voanews.com/ourworld or on your radio next Saturday and Sunday as we check out the latest in science and technology ... in Our World.